Interest in wireless communication, particularly personal wireless communication, increased more and more during the last few decades, and user demand for the ability to transmit and receive information wirelessly has proven insatiable. Driven by high and growing demand, developers and manufacturers are constantly seeking ways to increase the information that can be transmitted and received by network infrastructure and user equipment (UE). Finding such ways presents increasing challenges, as the desire of users for reliable, high quality service is accompanied by their reluctance to pay increased rates such as might be needed to finance new infrastructure to meet demands for service.
Techniques that allow for efficient use of equipment serve a number of goals. They allow providers to manage their costs, which may lead to increased profits, lower charges to users, or both. They allow providers to avoid the building of new infrastructure, thereby avoiding the need to petition governments for permits to build such infrastructure and avoiding resistance among the public. Efficient use of equipment can be expected to provide the full panoply of benefits that may be expected from increasing services without concomitantly increasing deployment of equipment.
The telecommunications industry is continually introducing techniques aimed at increasing efficiency and service levels. One such technique is orthogonal frequency division multiplexing (OFDM), which distributes data across subcarriers at closely spaced frequencies in order to achieve a higher overall data rate than the rate per subcarrier.
Another technique that is gaining attention is coordinated multipoint transmission, which is directed to coordination of communication to a given UE among different transmission points.
Wireless communication systems typically comprise numerous and widespread infrastructure elements, organized and allocated in various ways so that a particular UE is identified with the elements serving it at a particular time. Many UEs are served by different elements at different times. For example, a UE may switch between serving elements as it moves from one geographic location to another. Transmissions from elements serving one UE can have significant detrimental impacts on UEs being served by different elements, and coordinated multi-point communication allows for coordination of transmissions among elements to reduce such detrimental impacts and, indeed, to allow for improved transmission quality through simultaneous transmission of the same data to the same UE by multiple serving elements.
Many wireless communication systems are organized into cells. A cell may be thought of as a geographic region served by infrastructure identified with the cell. In one exemplary system, service is provided by transmission points distributed throughout the region served by the system, with each cell comprising at least one transmission point, and with each transmission point being associated with a cell.
Each cell and the transmission points within it may be associated with a cell identifier, and the transmission points and other elements associated with a cell may identify themselves to UEs as being associated with that cell. It will be recognized that transmission points may be allocated or identified in numerous ways, and that identification of transmission points with a cell is only one example of such allocation. A transmission point comprises a single antenna, or an array of co-located antennas. In one example, a cell may be served by a single transmission point, comprising a single array of co-located antennas, with the transmission point using an identifier associated with the cell. To take another example, a cell may be served by multiple transmission points, with each of the transmission points comprising an array of co-located antennas, and with each transmission point serving the cell using the same identifier to indicate its association with the cell. Each transmission point may also use its own individual identifier, used separately from and in addition to the cell identifier. One arrangement of multiple transmission points within a cell is the case of a cell using one or more central transmission points and one or more remotely located transmission points in the form of remote radio heads.
Transmission points serving various UEs may engage in coordination with one another in order to provide improved service. In joint processing, transmission points serving various UEs may engage in coordination with one another to cooperate in transmitting the same data to UEs, thereby reducing interference with one another and generally increasing spectral efficiency of the system. Various notable impacts on service may occur when a UE being served by a transmission point within one cell encounters transmissions directed to a UE within a different cell by a transmission point serving that cell, but it will be recognized that impacts on service may be caused by transmission points operating in the same cell or in systems in which transmission points are not allocated to cells, and coordination between transmission points may be used whenever appropriate whether the transmission points belong to the same cell or different cells, or whether the system is organized into cells at all.
In systems that are organized into cells, each cell is served by one or more transmission points, and the transmission points may coordinate communication with UEs in a number of ways directed to improve service. Coordination of communication can be expected to yield improvements by increasing the average cell throughput, and is also particularly useful in reducing interference encountered by UEs operating near the edges of cells, thereby enhancing the cell coverage A cell edge is a region between adjacent cells, so that UEs near an edge of a cell will be serviced by a transmission point serving the cell but can also be expected to be exposed to relatively strong signals from transmission points serving adjacent cells.
Such issues may also arise in cases in which UEs are within range of multiple transmission points generally, whether or not those transmission points belong to different cells. A transmission point can be expected to have an effective coverage area, with detectable transmissions extending beyond the effective coverage area. A UE being served by a first transmission point, but within a range at which it can detect signals from a second transmission point, may be subject to interference from the second transmission point whether or not the two transmission points happen to be serving different cells.
Transmission points serving various UEs may engage in coordination with one another in order to provide improved service. For example, in one technique known as coordinated scheduling/beamforming, transmission points may coordinate their scheduling or spatial precoding weights to reduce impacts on UEs they are not immediately serving. The transmission points may coordinate their scheduling and choice of precoding weights over each sub-band. Such coordinated scheduling of UEs over a sub-band helps to insure that the UEs experience minimal interference from one another and that each of the UEs experiences minimum interference from transmissions directed to a different one of the UEs.
In joint processing, transmission points may engage in coordination to jointly transmit data to the UE. Multiple transmission points within range of a UE may therefore serve the same UE at the same time and thus provide stronger signals rather than cause interference. Such a technique increases spectral efficiency of a communication system.